Bioefficacy and persistent toxicity of some insecticides against few agriculturally important insect pests
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Date
2020-10
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
A detailed investigation was undertaken to determine the bioefficacy of some insecticides and mixed formulations against Spodoptera litura (Fabricius) and Spilarctia obliqua (Walker); effect of sublethal concentrations on growth and developmental parameters of S. litura; effect on feeding behaviour of S. litura and persistent toxicity on brinjal (Solanum melongena L.) against Henosepilachna vigintioctopunctata (Fabricius). All the experiments were conducted in Insecticide Toxicology Laboratory of the Department of Entomology. The contact toxicity of dichlorvos and carbosulfan was tested against 7d old larvae (mean initial weight = 0.183g/ larva) of S. litura by topical application method using Hamilton microapplicator dispenser under laboratory conditions. The LD50 values of dichlorvos at 12 and 24 HAT were 3.9061 and 2.8419 μg/larva while the LD50 of carbosulfan at 36, 48, 72 and 96 HAT were 4.9041, 4.0578, 4.0954 and 3.4784 μg/larva, respectively. The LT30, LT50 and LT90 values of dichlorvos at 1.52 μg/larva were 16.47, 33.06 and 183.74h, respectively and for carbosulfan at 7.5μg/larva the respective values were 10.41, 21.20 and 121.99 h. In another experiment the LD30, LD50 and LD90 value of profenofos + cypermethrin and deltamethrin + triazophos at 24HAT were 0.8483, 1.5829 and 7.3489 μg/larva and 1.0312, 2.2669 and 15.7568 μg/larva respectively against 8d old larvae (mean initial
weight = 0.193g/ larva) of S. litura by topical application method using Hamilton microapplicator dispenser. Profenofos + cypermethrin was 1.24 (RT30), 1.43 (RT50) and 2.14 (RT90) times more toxic than deltamethrin + triazophos at different RT levels. LT50 values for profenofos + cypermethrin at 1.72, 1.32 and 0.88 μg/larva was 22.90, 27.83 and 37.34h respectively while the LT50 values for deltamethrin + triazophos at 2.16 μg/larva was 29.17h. In another experiment the contact toxicity of chlorpyrifos + fipronil was tested against 8d old larvae of S. litura by topical application method using Hamilton microapplicator dispenser under laboratory conditions. The LD values at 36, 48 and 72 HAT were 0.6779, 0.4995 and 0.4188 (LD30s); 1.4578, 0.9956 and 0.9103 (LD50s) and 9.5979, 5.4393 and 6.1538 μg/larva (LC90s) and the LT values at 1.926 and 2.889 μg/larva doses of chlorpyrifos +
fipronil were 20.92 and 14.85h (LT30s); 34.95 and 24.25h (LT50s); 123.61 and 83.38h (LT90s), respectively. The contact toxicity of dichlorvos was determined against 9d old larvae (mean initial weight = 0.118g/ larva) of S. obliqua by topical application method using Hamilton microapplicator dispenser. The LD30, LD50 and LD90 values of 48 HAT were 1.8710, 3.4271 and 15.2026 μg/larva, respectively. The LT values at the dose of 3.04 μg/larva of dichlorvos were 21.99h (LT30); 45.13h (LT50) and 264.75h (LT90), respectively. The effect of sublethal concentrations of three insecticides viz. chlorpyrifos + fipronil, fipronil and chlorpyrifos on growth and development parameters was tested against 6d old larvae (average larval weight: 0.0184g) of S. litura by leaf smear method on castor leaf disc. At 4 days after feeding (DAF), the highest reduction (21.03%) in mean weight gain over control was observed in the highest concentration of chlorpyrifos (0.01%) which resulted in mortality of 33.33%. Pupation percentage was highest (80.95%) in the lowest concentrations of chlorpyrifos (0.0001%) than fipronil 0.0001% (76.19%). In comparison of control
(0.214g/pupa), 1.57 times lower pupal weight was observed in chlorpyrifos 0.01% (0.136g/pupa). The feeding inhibitory activity of three insecticides viz. chlorpyrifos + fipronil, fipronil and chlorpyrifos were determined against 6d old larvae (average larval weight: 0.0184g) of S. litura by leaf smear method on castor leaf disc. The order of deterrence at the higher concentration (0.01%) was; chlorpyrifos > chlorpyrifos + fipronil > fipronil, however at lower concentrations (0.001 and 0.0001%) the order was chlorpyrifos+fipronil > fipronil > chlorpyrifos. The persistent toxicity of two insecticides viz. chlorantraniliprole and flubendiamide have been determined on brinjal against 3d old grubs (average grub weight = 0.0013g/grub) of H. vigitioctopunctata. Chlorantraniliprole @ 0.01% was the most persistent insecticide with a PT value of 1026.52 followed by flubendiamide @ 0.01% (932.2), chlorantraniliprole @ 0.008% (755.4) and flubendiamide @ 0.008% at 24 HAF. After 72 hours of feeding on the treated leaves, chlorantraniliprole @ 0.01% again showed highest PT value of 2000.0 followed by chlorantraniliprole @ 0.008% (1634.16), flubendiamide @ 0.01% (1613.26) and flubendiamide @ 0.008% (1400.00).